The present invention generally relates to computer local area networks, and more particularly to node devices having Media Dependent Interfaces (MDI) that are installed in such networks and their automatic connection configuration.
Many local area network products (LAN) use a medium consisting of twisted copper wire pairs for the transmission and reception of data. It is generally a requirement that one or more pairs be used for transmission of data in one direction and one or more other pairs to receive data in the opposite direction. The connection between two node devices is a link. For LAN technologies which employ a full-duplex medium, many have different pairs for transmission than for reception and thereby require that each end of the link use a defined assignment for its twisted pair connector to a particular pair of wires. For example, a Network Interface Card (NIC) is usually employed as an end node device, while a switch or a repeater will be employed as a concentrator or central component in a star-based network. For the link to operate, the NIC must transmit on a pair of wires that is connected to the receiver of the hub or switch and the NIC""s receiver must be connected to the transmitter at the other end of the link. If the transmit pair of wires of a device are connected to the transmit connectors of the connected device, the communication link will obviously fail.
Most LAN standards address this by assigning different connector pins to the wires in the twisted pair which is typically referred to as the Media Dependent Interface (MDI). In the IEEE-802.3""s 10BASE-T standard, an end node will assign pins 1 and 2 to the transmit pair while pins 3 and 6 are for connection to a twisted pair for receiving. The hub, which is typically a repeater or a switch for a 10BASE-T network, will assign its transmitter to pins 3 and 6 while its receiver will be connected to pins 1 and 2. This works quite well for configurations where NIC""s are attached to repeaters, but there are a few cases that become more important to consider with the emergence of switched networks. First there is a case where the NIC is connected directly to another NIC, or a repeater is connected to a repeater or a repeater is connected to a switch. Depending upon the assignment of pins at the network interface, it may become necessary to employ a crossover cable to address the fact that both products employ the same pin designations on their interfaces.
Some products will use a manual xe2x80x9cMDIXxe2x80x9d switch, with MDIX being a hub, repeater or switch configuration as opposed to an end node device, which is known as a MDI configured device. The switch allows the products to connect to other similar devices but requires an installer to manually push a button. The approach worked well for limited applications like a repeater-to-repeater port, but not in the general case where it is desired to build a produet that attaches to either a repeater, NIC or switch without manual intervention.
This resulted in the development of bus switches for making a solid state version of a crossover type circuit that used a low frequency alternating pin selection to perform an automatic operation. However, the product had the drawback that if two such devices were attached together, they could potentially get into a xe2x80x9clock stepxe2x80x9d operation where the necessary connections for establishing a communication link became impossible. Subsequently other products were developed which employed a similar algorithm and were forced to use a different alternation rate to avoid the lock step phenomena. While that worked for a limited set of products, it did not solve the general case whereby a guaranteed connection between nodes was achieved regardless of the manufacture or the model of product that was being used.
Accordingly, it is a primary object of the present invention to effectively solve the problem of lock step interaction in an improved automatic media connection apparatus which can effectively be used with products of well known manufacturers.
It is another object of the present invention to provide such an improved apparatus by using a pseudo-random generating element, in addition to an actual random elements to provide an implementation of an auto-MDIX/MDI algorithm that is virtually impossible to be placed in a lock step condition.
Yet another object of the present invention is to provide such an improved apparatus that is inexpensive to implement. The low cost is achieved by utilizing logic elements that exist in many node devices, so that software, or very minor hardware implementations comprise the essential cost that is involved.
Still another object of the present invention is to provide such an improved apparatus which is robust in its functionality and requires no user or customer intervention and which is operable whenever a device embodying the present invention is added to a network. Once the physical connections are made and the apparatus powered up, proper configuration is virtually assured.
These and other objects will become apparent upon reading the following detailed description, while referring to the attached drawings, in which:
FIG. 1 is a schematic diagram of the prior art and showing a media dependent interface 10BASE-T network interface card connected to a similar hub interface card;
FIG. 2 is a schematic diagram of the prior art and showing two 10BASE-T media dependent interface hubs connected together with a crossover connection to establish and maintain the communication links;
FIG. 3 is a perspective view of a female media dependent interface connector of the type which has pin connectors pursuant to the requirements of section 3FIGS. 1-4 of IEC603-7, detail specification for connectors;
FIG. 4 is a plug connector adapted for use to connect with the female connector shown in FIG. 3;
FIG. 5 is a table identifying the assignment of PHY signals to MDI and MDI-X pin identification and configuration;
FIG. 6 is an electrical schematic diagram of a network interface card in conjunction with a media switch, a processor and associated circuitry which forms a part of the preferred embodiment of the present invention;
FIG. 7 is a schematic diagram of a state machine which represents the logic of the operation of the apparatus embodying the present invention; and,
FIG. 8 is a chart illustrating the probability of not establishing a communication link versus time.